Sema: copy pointer alignment to struct field pointers

src/Module.zig

@@ -991,6 +991,7 @@ pub const Struct = struct {
         is_comptime: bool,
 
         /// Returns the field alignment. If the struct is packed, returns 0.
+        /// Keep implementation in sync with `Sema.structFieldAlignment`.
         pub fn alignment(
             field: Field,
             mod: *Module,